Optical patches are usually manufactured using casting, injection or embossing processes. When implementing these processes, two mould inserts corresponding respectively to the front surface and the rear surface desired for the optical patch are placed in a mould or an embossing device. In the context of the present specification, the phrase “mould insert” encompasses a casting insert, an injection insert, as well as an embossing insert. The optical patches produced in this way reproduce the insert surfaces. The issue is then to supply the mould inserts necessary for all the optical patches to be manufactured. But manufacturing a mould insert itself is costly, in particular for those of the mould inserts which have the Fresnel structure.
In addition, optical patches corresponding to all possible ophthalmic prescriptions need to be available, for satisfying all the needs that may occur with a great number of wearers. Typically, the ophthalmic prescriptions may correspond to values for the optical power from −4 diopters to +4 diopters with 0.25 diopter increment. Simultaneously, the prescribed astigmatism values may be from 0 to 1.0 diopter with increment of 0.25 diopter. This leads to a total number of 33×5, i.e. 165 possible prescription combinations. Then, supposing that all optical patches have one and same front surface, and that the rear surface alone produces the varying optical power and astigmatism values, then a total number of 166 mould inserts are necessary: one single front mould insert and 165 rear mould inserts. Such number of mould inserts is huge and very expensive as a consequence.
Then, an object of the invention consists in determining front and rear surfaces for a set of optical patches, so that every ophthalmic prescription can be satisfied with a limited total number of mould inserts.